1. Field of the Invention
This invention relates to a zoom lens and an image pickup apparatus. Specifically, the present invention relates to a technical field of a small-sized wide-angle zoom lens suitable for use with a small-sized image pickup apparatus such as a digital still camera and a video camera and also to an image pickup apparatus.
2. Description of the Related Art
Although an image pickup apparatus such as a digital still camera or a digital video camera has been miniaturized and become widespread for home use in recent years, further miniaturization is demanded for such image pickup apparatus. Accordingly, also for an image pickup lens incorporated in such image pickup apparatus, particularly also for a zoom lens, miniaturization by reduction of the overall length or the depth is demanded.
Particularly for a zoom lens for a digital still camera, also improvement in lens performance is demanded in addition to miniaturization in conformity with increase of the number of pixels of a solid-state image pickup device such as a CCD (Charge Coupled Device) device or a CMOS (Complementary Metal-Oxide Semiconductor) device.
Further, it is recently demanded strongly also to increase the power variation and the angle of view for image pickup at a wide angle end of a zoom lens.
A compact type digital still camera is available which incorporates a zoom lens whose power variation ratio is approximately 3 to 5 times. For a compact type digital still camera, it is demanded that it can be carried easily. Thus, it is necessary to reduce the thickness of an image pickup apparatus and a zoom lens in a thicknesswise direction, that is, in the direction of an optical axis from an image pickup object to the image pickup lens when the image pickup object stands facing the image pickup apparatus.
As a zoom lens suitable for reduction in thickness in the thicknesswise direction of an image pickup apparatus and the zoom lens, a zoom lens has been proposed which includes a bending optical system wherein an optical member for bending the optical axis by 90° is disposed in a first lens group. A zoom lens of the type just described is disclosed, for example, in Japanese Patent Laid-Open No. 2006-64839 (hereinafter referred to as Patent Document 1) or Japanese Patent Laid-Open No. 2006-276475 (hereinafter referred to as Patent Document 2).
The zoom lens disclosed in Patent Document 1 has a four-group configuration including a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power and a fourth lens group having a positive refracting power. In the zoom lens disclosed in Patent Document 1, a prism as the optical member for bending the optical axis by 90° is disposed between a negative lens and a positive lens of the first lens group to achieve reduction in thickness in the thicknesswise direction of the image pickup apparatus and the zoom lens.
The zoom lens disclosed in Patent Document 2 has a five-group configuration including a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, a fourth lens group having a positive refracting power and a fifth lens group having a positive refracting power. The zoom lens disclosed in Patent Document 2 includes a camera shake correction mechanism which has a bending optical system and includes a positive lens disposed in a fifth lens group for shifting in a direction perpendicular to the optical axis to correct an image against a shake.